Fixed hanging scripts trying to parse stderr

code.py, specifically, was getting messed up by inconsequential GCC
objdump errors on Clang -g3 generated binaries.

Now stderr from child processes is just redirected to /dev/null when
-v/--verbose is not provided.

If we actually depended on redirecting stderr->stdout these scripts
would have been broken when -v/--verbose was provided anyways. Not
really sure what the original code was trying to do...

scripts/cov.py

@@ -227,7 +227,7 @@ def collect(gcda_paths, *,
             print(' '.join(shlex.quote(c) for c in cmd))
         proc = sp.Popen(cmd,
             stdout=sp.PIPE,
-            stderr=sp.PIPE if not args.get('verbose') else None,
+            stderr=None if args.get('verbose') else sp.DEVNULL,
             universal_newlines=True,
             errors='replace',
             close_fds=False)